Thermal ink jet print is a commonly used method of recording images on recording material, such as paper or cloth, by discharging discrete droplets of ink from nozzles of a print head and allowing these droplets to be absorbed by the recording material. Thermal ink jet recording offers opportunities for quiet, high speed, full color printing. Also, images printed with thermal ink jet printers seldom need to be fixed or treated after the ink droplets are absorbed on the recording material.
Thermal ink-jet printing is a non-impact printing process in which ink droplets are formed and thereafter deposited on a print medium in a particular order to form an image on the print medium. The low cost and high quality of the printed output in combination with the relatively noise-free operation of ink jet printers have made ink jet printing a popular and economical alternative to other types of printing in consumer, office, and industrial settings.
Thermal ink-jet printing is one example of a drop-on-demand form of non-impact printing. Other examples of drop-on-demand systems, besides thermal ink jet, are piezoelectric ink jet, acoustic ink jet, and vibrating ink jet systems. Besides drop-on-demand systems, there are also continuous stream ink jet printing systems. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream of ink is then broken up into droplets at a fixed distance from the orifice, and the ink droplets are thereafter directed toward the recording medium or recycled into the printing ink supply.
In drop-on-demand systems, an ink droplet is not formed or expelled from the print head unless the droplet is to be placed on the recording medium. Therefore, since drop-on-demand systems require no ink recovery or post-ejection treatment, drop-on-demand systems are typically somewhat simpler in construction and operation than continuous stream ink jet printing systems. Thermal ink jet (sometimes referred to as xe2x80x9cbubble jetxe2x80x9d) systems are one of the most common types of drop-on-demand ink jet printing systems.
In thermal ink jet printing, the energy for drop formation and ejection is generated by electrically heated resistor elements. The resistor elements heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble. Superheating of the ink far above the normal boiling point of the ink causes the bubble formation. The expansion of the bubble forces a droplet of ink out of a nozzle at a high rate of speed toward the recording medium. After the collapse of the bubble, the ink channel proximate the resistor elements refills by capillary action.
Colorants for inks printed by thermal ink jet printing may be generally classified as dyes or pigments. Accordingly, thermal ink jet printer inks may incorporate dye(s), pigment(s), or a combination of dye(s) and pigment(s) to print images on the recording media. Of these three, dye-based thermal ink jet printer ink compositions are most widely available commercially.
Dye-based thermal ink jet inks currently in use in the industry demonstrate an inability to achieve acceptable results on both coated silk and coated cotton substrates. The present invention relates to a thermal ink jet printer ink that may incorporate a direct dye. The present invention further relates to a dye-based, thermal ink jet printer ink with the ability to form printed images on a variety of textile medias.
The present invention includes a method of making a ink jet ink. The method entails combining a water miscible organic solvent, water, and a dye, and blending the water miscible organic solvent, the water, and the dye together to form the ink jet ink. The ink jet ink produced by this method is capable of forming a printed image on a variety of coated textiles and cloths. The present invention further includes a method of forming a printed image on a recording medium and a thermal ink jet ink.
The present invention generally concerns a technique for preparing dye-based ink jet inks for use in thermal ink jet printers. The ink of the present invention is beneficially applicable to a variety of coated textiles. More specifically, a particular ink of the present invention can be applied to both coated silk and coated cotton textiles with acceptable results, despite differences between the substrates. This is an advance over the inability of prior dye-based thermal ink jet inks to achieve acceptable results on both coated silk and coated cotton textile substrates. This beneficial property of the inventive ink is believed to be due, in substantial part, to the use of direct dyes as opposed to anionic, cationic, reactive or dispersive dyes. The applicability of the inventive ink to both coated silk and coated cotton textile substrates the ink is attributable to the formulation and dye selection for the inventive ink. The inventive ink is achieved using relatively inexpensive components that are combined using simple equipment via a very simple mixing procedure.
The ink of the present invention includes, at a minimum, water, a water miscible organic solvent, and dye. The dye may be provided as part of a dye solution. The dye solution that may be incorporated as part of the ink of the present invention includes both a dye and a liquid carrier for the dye, typically water. The dye is usually obtained from a commercial source in prepared form. Some examples of suitable, commercially available, dyes include Direct Yellow 132 Dye that is available from Tricon Colors LLC of Elmwood Park, N.J.; Intrajet Liquid Magenta DJL that is available from Crompton and Knowles Colors Incorporated of Charlotte, N.C.; and Duasyn Direct Turquoise Blue FRL-SF Liquid and Duasyn Direct Black HEF-SF Liquid that is available from Clariant Corporation of Coventry, Rhode Island.
The dyes that are included in the inks of the present invention preferably have a nominal particle size of about 0.1 microns or less, and are salt free to enhance the excellent transparency of the inventive inks. To ensure that the dyes, and other components, have not contained any large particulate contamination, it is recommended that the ink be filtered through a 0.45 micron polytetrafluroethylene (PTFE) filter prior to placing the ink in the printing device, such as a thermal ink jet printer.
Some non-exhaustive examples of the water miscible organic solvent of the ink of the present invention include ethers, such as tetrahydrofuran, dioxane, glycol ether, etc.; oxyethylene or oxypropylene addition dimers, trimers, or polymers, such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol, etc.; alkylene glycols having an alkylene group of 2 to 6 carbons, such as ethylene glycol, propylene glycol, trimethylene glycol, butylene glycol, 1,2,6-hexanetriol, hexylene glycol, etc.; thiodiglycol; glycerin; lower alkyl ethers of a polyhydric alcohol, such as ethylene glycol monomethyl (or monoethyl) ether, diethylene glycol monomethyl (or monoethyl) ether, triethylene glycol monomethyl (or monoethyl) ether, propylene glycol monomethyl (or monoethyl) ether, dipropylene glycol monomethyl (or monoethyl) ether, tripropylene glycol monomethyl (or monoethyl) ether, etc.; lower dialkyl ethers of a polyhydric alcohol, such as triethylene glycol dimethyl (or diethyl) ether, tetraethylene glycol dimethyl (or diethyl) ether, etc.; sulfolane; 1,3-dimethyl-2-imidazolidinone; and any of these in any combination.
The concentration of the water miscible organic solvent in the ink of the present invention may generally range from about 2% to about 30%, by weight, based on the total weight of the ink. The concentration of the water miscible organic solvent in the ink more preferably ranges from about 5% to about 20% by weight, based on the total weight of the ink. The concentration of the water miscible organic solvent in the ink most preferably ranges from about 10% to about 15%, by weight, based on the total weight of the ink.
Any of the water miscible organic solvents listed above may be used individually or may be used in combination as the water miscible organic solvent component of the ink. When used in combination, the various examples of the water miscible organic solvent that are listed above may be used together in any combination. However, the water miscible organic solvent of the ink preferably includes a high-boiling, water miscible organic solvent that is selected from oxyethylene or oxypropylene addition dimers, trimers, or polymers, lower alkyl ethers of a polyhydric alcohol, and any of these in any combination.
A xe2x80x9chigh-boiling,xe2x80x9d water miscible organic solvent is a water miscible organic solvent with a boiling point, at 1 atmosphere of gauge pressure, that is greater than the boiling point of water ( greater than 212xc2x0 F.). The water and the high-boiling water miscible organic solvent forms a eutectic mixture. The high-boiling water miscible solvent is believed to control the rate of evaporation of water from the ink. By controlling the water evaporation rate, the high-boiling water miscible solvent is consequently thought to help maintain uniform dispersion of the dye in the ink, even during and after formation of ink droplets.
Distilled or deionized water is commonly used. The water that is used in combination with the water miscible organic solvent and the dye may be present in the ink of the present invention at a concentration ranging from about 5% to about 95% by weight, based on the total weight of the ink. More preferably, the water is present in the ink of the present invention at a concentration ranging from about 35% to about 90% by weight, based on the total weight of the ink. Most preferably, the concentration of the water in the ink ranges from about 70% to about 90% by weight, based on the total weight of the ink.
The dye that is combined with the water miscible organic solvent and the water to form the ink of the present invention, depending upon the particular dye selected for the ink, may generally be present in the ink from about 0.1% to about 55% by weight, based on the total weight of the ink. For example, yellow ink may be made to contain from about 0.1 to about 30 weight percent of the yellow dye when the yellow dye is the Direct Yellow 132 Dye, magenta ink may be made to include from about 0.1 to about 45 weight percent of the magenta dye when the magenta dye is the Intrajet Liquid Magenta DJL, cyan ink may be made to include from about 0.1 to about 45 weight percent of the dye when the cyan dye is the Duasyn Direct Turquoise Blue FRL-SF Liquid, and the black ink may be made to include from about 0.1 to about 55 weight percent of the black dye when the black dye is the Duasyn Direct Black HEF-SF Liquid.
The components of the ink are selected so that these components do not cause or support precipitation or separation of the dye. Dipropylene glycol is the preferred high-boiling water miscible organic solvent for use in the ink because dipropylene glycol has been found to serve as a humectant that tends to help prevent clogging and plugging of jetting nozzles in ink jet printers. Lower alkyl ethers of a polyhydric alcohol, such as dipropylene glycol monomethyl ether, are preferred examples of the high-boiling water miscible organic solvent since lower alkyl ethers of a polyhydric alcohol, such as dipropylene glycol monomethyl ether, are thought to enhance adhesion of the ink to textile substrates on which the ink is applied. Also, lower alkyl ethers of a polyhydric alcohol are thought to help maintain uniform dispersions of the dye in the ink, even after formation of the ink droplets and application of the ink droplets to the recording medium.
Though surfactants may be incorporated into the ink of the present invention, surfactants are preferably excluded from the ink. The role of any surfactant included in the ink is to reduce the surface tension of the liquid components of the ink to help enhance dispersion of the dye in the ink. For many dyes, such use of surfactant is not believed necessary to maintain dispersion of the dye in the ink. Nonetheless, it is permissible to include surfactant in the ink at a concentration ranging from about 0.1 weight percent to about 1.0 weight percent, based upon the total weight of the ink. Some commercially available dyes are believed to contain surfactant. Also, some examples of water-miscible surfactants that may permissibly be included in the ink are (1) surfactants from the SURFYNOL(copyright) line of surfactants that are available from Air Products and Chemicals, Inc. of Allentown, Pa. and (2) surfactants from the TERGITOL(copyright) line of surfactants and from the TRITON(copyright) line of surfactants that are each available from Union Carbide, Inc. of Danbury, Conn. Some non-exhaustive examples of suitable SURFYNOL(copyright) surfactants include the SURFYNOL(copyright) 440, 502, and 504 surfactants. Some non-exhaustive examples of suitable TERGITOL(copyright) surfactants include the TERGITOL(copyright) 15-5-7 and 15-5-9 surfactants. Some non-exhaustive examples of suitable TRITON(copyright) surfactants include the TRITON(copyright) CF-10, CF-21, and XL-80N surfactants.
Besides the water miscible organic solvent, water, and dye, the ink of the present invention may additionally include a biocide to enhance the long-term stability of the ink versus any detrimental biological organisms that may be present. An example of a suitable, commercially available biocide is Proxel GXL available from Zeneca Incorporated of Wilmington, Del. Most preferably, the concentration of the biocide in the ink ranges from about 0.05% to about 0.2% by weight, based on the total weight of the ink.
The ink of the present invention that is described above is particularly suited for use in a thermal ink jet printer, such as a bubble jet printer. However, if it is desired, the ink of the present invention may be modified to permit use of the inventive ink in other types of ink jet printers, such as a piezo ink jet printer. This modification for piezo ink jet printing entails the addition of a quick drying water soluble polymer, such as an acrylic polymer. However, for use in thermal ink jet printing, water-soluble polymer, such as the acrylic polymer, is preferably not included in the ink of the present invention, since such water-soluble polymer will detract from the otherwise beneficial properties of the inventive ink in relation to thermal ink jet printing.
Beneficially, the inks of the present invention are capable of being used in high-speed thermal ink jet printing to produce, after drying of the printed ink, circular-shaped dots that are substantially free, and preferably are entirely free, of ragged edges. When the inks of the present invention are used together in an ink set of a thermal ink jet printer, with the different inks of the ink set containing different dyes and/or different concentrations of dye, each of the ink sets are capable of being used in high-speed thermal ink jet printing to produce circular-shaped dots that have about the same diameter as dots produced with other inks of the particular ink set.
To support high-speed jetting of the ink out of the thermal ink jet printer ink chamber, the ink produced in accordance with the present invention preferably should have a low Brookfield viscosity ranging from about 1.0 centipoise to about 4.0 centipoise at an ink temperature of about 25xc2x0 C. More preferably, the ink should have a Brookfield viscosity ranging from about 1.0 centipoise to about 3.0 centipoise at an ink temperature of about 25xc2x0 C. Still more preferably, the ink of the present invention should preferably have a Brookfield viscosity ranging from about 1.5 centipoise to about 2.5 centipoise at an ink temperature of about 25xc2x0 C. The ink viscosity is determined using a Brookfield Model DV-III programmable rheometer equipped with an adaptor for small samples. The Brookfield Model DV-III rheometer is available from Brookfield Engineering Laboratories, Inc. of Stoughton, Mass.
The viscosity (the xe2x80x9cBrookfield viscosityxe2x80x9d) of a particular ink sample is determined with the ink sample at room temperature (about 25xc2x0 C.). About 5 grams of the particular ink being tested are placed in the small sample adaptor which is positioned within the viscosity measurement cell of the rheometer. An appropriate spindle, identified by a spindle number and selected so that the measured viscosity is within the range of the particular spindle, is positioned within the small sample adaptor within the measurement cell. The Brookfield viscosity is measured while running the selected spindle at a revolution per minute (RPM) rate selected based upon calibration studies conducted at the direction of the inventor. For all viscosity determinations and specifications of this disclosure, Spindle No. 18 is selected and is rotated at about 225 RPM during viscosity determinations, unless otherwise indicated.
Also, each ink produced in accordance with the present invention should have a surface tension of about 30 to about 74 dynes per centimeter at an ink temperature of about 25xc2x0 C, with the surface tension more preferably ranging from about 40 to about 60 dynes per centimeter. Most preferably, the ink should have a surface tension of about 50 to about 55 dynes per centimeter at an ink temperature of about 25xc2x0 C. to enhance the compatibility and the uniform laydown of the inventive ink on any coating that is present on the recording media. Unless otherwise indicated, all surface tension values recited herein were determined with or are based upon use of the DuNOUY interfacial tensiometer that is available from CSC Scientific Company, Inc. of Fairfax, Va. using the surface tension measurement procedures set forth in the instructions accompanying the DuNOUY interfacial tensiometer. All surface tension values recited herein were determined at or are based upon an ink sample temperature of about 25xc2x0 C.
When the ink of the present invention is prepared as a plurality of different inks for use as an ink set of an ink jet printer, the low viscosity of the individual inks of the ink sets aids in producing dots of about the same diameter for each ink of the ink set. Ordinarily, different interactions of the individual dots with the recording medium by virtue of the surface tension of the different inks, absent some type of off-setting influence, would cause individual dots formed from different inks to vary in height and to have somewhat different diameters. However, formulation of the inks to have a low viscosity offsets affects of the surface tension of the individual inks and permits individual dots of the different inks to flatten out on the recording medium in the desired circular shape. Additionally, the actual surface tension and viscosity are carefully balanced in each of the different inks of the ink set to give the printed dots of each of the different inks of the ink set about the same diameter, such as about 4 mils to about 5 mils, when printing via thermal ink jet printing on the recording medium.
Inks that are produced in accordance with the present invention have been found to be highly transparent. The dyes that are used in the ink of the present invention, as specified above, helps to enhance the transparency of the inventive inks. Additionally, since transparency is also a measure of impurities, such as salts within the ink, selection of the ink components based on a high transparency value helps minimize impurity levels in the ink. Minimization of impurities in the ink helps to optimize printer head performance by minimizing precipitation and plating of impurities on the printer head of the ink jet printer. Minimization of precipitable impurities also extends the life of the printer heads. The liquid conductivity of individual inks produced in accordance with present invention should preferably be about 10 milli-mhos, or less, to ensure that impurity levels are held at acceptably low levels. More preferably, the ink of the present invention should have a liquid conductivity of about 5 milli-mhos, or less, to further minimize impurity levels in the ink. Unless otherwise indicated, all liquid conductivity determinations recited herein were determined or are based upon use of a Model No. 01481-61 Conductivity Meter that is available from Cole-Parmer Instrument Co. of Vernon Hills, Ill. using the procedure set forth in the instructions accompanying the Model No. 01481-61 Conductivity Meter. All liquid conductivity values recited herein were determined at or are based upon an ink sample temperature of about 25xc2x0 C.
Additionally, the ink produced in accordance with the present invention must be compatible with thermal ink jet printer components. Besides having a low level of impurities to enhance printer head operation and extend printer head life, the ink produced in accordance with the present invention preferably has a pH in the range of about 6.5 to about 8.5 to minimize the potential for corrosion of metallic materials that are sometimes used in printer head construction and that are subject to corrosion in acidic environments. Unless otherwise indicated, all pH determinations recited or specified herein are based upon use of the Oakton Model No. WD-35617-02 Digital Benchtop pH/mV/xc2x0 C. Meter that is available from Cole-Parmer Instrument Co. of Vernon Hills, Illinois using the procedure set forth in the instructions accompanying the Model No. WD-35617-02 Digital Benchtop pH/mV/xc2x0 C. Meter. All pH values recited herein were determined at or are based upon an ink sample temperature of about 25xc2x0 C.
An additional consideration is that the dyes and other components used in the ink of the present invention should be thermally stable, and thus not subject to thermal decomposition, at temperatures ranging up to about 300xc2x0 C., which is the maximum temperature typically experienced by inks in printer heads of thermal ink jet printers.
Inks that are prepared in accordance with the present invention are capable of drying very quickly, typically within less than about one minute, without any post treatment of the printed ink, such as application of hot air to the ink, and consequently permit high speed ink jet printing of multiple dot layers on the recording medium. If desired, hot air may be applied to the ink to further accelerate drying of the ink. However, such application of hot air is not essential to attaining quick ink drying rates.
The inks of the present invention are considered to be dry when the printed ink is free of tackiness and does not smear with application of finger pressure. Again, even without application of any post-treatment, such as application of hot air, the inks of the present invention typically meet this standard of dryness within less than about one minute after being printed on the recording medium.
One net effect of the process of preparing individual inks, including individual inks of an ink set, in accordance with the present invention is that each ink may have very similar performance characteristics within a relatively narrow range so that the jetability, the speed of ink jet printing, and the printed dot sizes and shapes of the different inks are essentially the same for each different ink. This is true, even though different dyes are used in making different inks and even though inks of the same color may have different dye concentrations, since the dye of each different ink produced in accordance with the present invention makes up only a small percentage of each of the different inks. Forcing the individual inks to have similar performance properties in this manner simplifies the process of ink jet printing, especially when using inks sets that contain multiple inks of the present invention, because this use of inks with similar performance characteristics between different inks negates any need to compensate for differences, other than color, between different inks.
The process of making the inks of the present invention is simple and straightforward, and does not require any complex, expensive processing equipment or procedures. First, all of the components of the ink, such as the water, water miscible organic solvent(s), dye, biocide, and any optional ingredients (surfactant, for example) are combined together in a mixing container. Thereafter, the combined components are blended together using any commercially available, low shear, mixing apparatus that does not promote foaming. One suitable low shear mixing technique merely entails slowly stirring the various ink components together to effect blending.
Next, air bubbles that may have been introduced during the mixing of the components can be removed from the ink by vacuuming the ink in accordance with standard and well known procedures for vacuuming inks. The vacuuming of the ink may be accompanied by use of any conventional ultrasonic vibration source in the ink to speed up the removal of trapped air bubbles. Next, after removal of any trapped air bubbles, the ink is preferably further treated by filtering through an appropriate filter media with a nominal pore size of 0.45 microns.